Generally, it is known in the art that incremental position encoders are of two common types, linear and rotary.
The linear type of encoder, for example as disclosed in U.S. Pat. Nos. 2,848,698 and 3,245,144, senses increments of position along the axis of freedom as well as the limits of movement. A linear scale is provided and the encoder resolves scale divisions in the axis upon the occurrence of relative movement between the encoder body and the scale.
The rotary type of encoder, such as taught in U.S. Pat. No. 3,262,105, does not measure or sense increments of position directly along an axis. It has a rotatable circular scale which is driven by a screw (or the motor which drives the screw) which, for example, drives a carriage in an axis. The rotary encoder then senses increments of angular displacement of the scale measured on the periphery of the scale rotor as well as revolutions of the scale.
Linear encoders have found application in printer technology, such as disclosed in U.S. Pat. Nos. 4,786,803 and 4,789,874 by Majette et al. for a single channel encoder system for controlling the position, velocity and direction of a media scanning printhead.
Thus, encoders known in the art are relatively complex in that the functions for which they are employed often require a scale member. Yet, encoders also may be useful for the determination of a digital state condition. For example, a digital state condition detection is useful to detect a "PAPER FULL" condition in a collating or sorting unit in hard copy production, such as computer printers and electrophotography copiers. Furthermore, network printing is stressing the need for unattended printing processes. Devices for this type of state condition sensing can be critical to system operations and management.
Therefore, there is a need for improvement in the field of encoders.